Aerials & Electronics

I have three aerials on my recently purchased trawler, along with a number of other electronic receivers/transmitters. I'm still working my way through the boat and have a few lingering questions:

- I understand a separate aerial is required for each VHF, which accounts for 2 aerials, so I assume the 3rd is for use as an FM radio antenna. There are 2 un-used coax cables in the boat (2nd photo) - one of those is definitely for the TV receiver (which we don't use). Does anyone know if the 2nd might be for the extra aerial? Do aerials typically have a coax connection? Would it be common practice to get an adapter from coax to stereo antenna?

- How would I test these connections to see which does what? It's a bit difficult to physically trace these - I could test by plugging into the antenna port for my stereo I suppose. Any other suggestions?

- There are 2 very small receivers on my radar arch - see photo. One at the very top and one lower. I believe at least one of these would be for the chart plotter GPS receiver, any ideas what the other one is for? AIS? Or possibly for the 2nd chart plotter, although that one is slaved to the first.

Thanks!

Congrats on your new boat. As to the antennas, could be a lot of things. My AIS antenna looks just like a VHF antenna but only 4’ tall. When I bought my boat it literally had 12 unused antenna mounts on it. Who knows why, why they wouldn’t just use an existing mount when they wanted to add an antenna. And the marina told me that they had removed several and patched the holes.

The small “receivers” are likely GPS antennas. Navico has a heading sensor that looks similar, so that would be a second guess if you have any Lowrance/Simrad/B&G electronics.

Thanks, I have a Raymarine autopilot - could it be for that?

I doubt it, but I only had 2 generations of Raymarine and don’t know all of them.

One thing you can try is to make sure everything is powered down and try a "tone" "ringer" wire tracer like this one

Sperry Instruments ET64220 Wire Tracker Wire Tracer, Audio / Video Installers Must-Have, for Coax, CAT 5, Speaker & Phone, Adapter plugs: RJ-45, RJ-11, Coax & More https://www.amazon.com/dp/B00279JLBQ/ref=cm_sw_r_em_apa_i_pKv8FbHA5VZ6F

There are many varieties. Mine is years old. I just posted 5he 1st one I saw on Amazon.

rherten said:

I have three aerials on my recently purchased trawler, along with a number of other electronic receivers/transmitters. I'm still working my way through the boat and have a few lingering questions:

- I understand a separate aerial is required for each VHF, which accounts for 2 aerials, so I assume the 3rd is for use as an FM radio antenna. There are 2 un-used coax cables in the boat (2nd photo) - one of those is definitely for the TV receiver (which we don't use). Does anyone know if the 2nd might be for the extra aerial? Do aerials typically have a coax connection? Would it be common practice to get an adapter from coax to stereo antenna?

- How would I test these connections to see which does what? It's a bit difficult to physically trace these - I could test by plugging into the antenna port for my stereo I suppose. Any other suggestions?

- There are 2 very small receivers on my radar arch - see photo. One at the very top and one lower. I believe at least one of these would be for the chart plotter GPS receiver, any ideas what the other one is for? AIS? Or possibly for the 2nd chart plotter, although that one is slaved to the first.

Thanks!

Click to expand...

If you have AIS, yes a typical installation is a dedicated VHF antenna (usually shorter, say 4' or so) and a dedicated GPS mushroom. I think that's best practices, though, not necessarily mandatory... and it is technically possible to piggy-back two functions (normal marine VHF and AIS VHF) on a single antenna.

I wouldn't expect a VHF antenna to be for FM radio. OTOH, I think there are some whip antennas cut for VHF/UHF and used for TV and AM/FM radio... so if you don't have a small dish-like thing (e.g., Glomex or Shakespeare) AM/FM/TV antenna, could be one of your whips is for that.

All of the whips would likely use CoAx to feed follow-on systems (marine VHF, tuners, TVs, stereo radio, etc.).

The middle whip in your pic looks to have an appendage I don't recognize... Any brand name/model info on that?

One cheap way to trace is to first determine what works and what doesn't.

-Chris

ranger42c said:

If you have AIS, yes a typical installation is a dedicated VHF antenna (usually shorter, say 4' or so) and a dedicated GPS mushroom. I think that's best practices, though, not necessarily mandatory... and it is technically possible to piggy-back two functions (normal marine VHF and AIS VHF) on a single antenna.

I wouldn't expect a VHF antenna to be for FM radio. OTOH, I think there are some whip antennas cut for VHF/UHF and used for TV and AM/FM radio... so if you don't have a small dish-like thing (e.g., Glomex or Shakespeare) AM/FM/TV antenna, could be one of your whips is for that.

All of the whips would likely use CoAx to feed follow-on systems (marine VHF, tuners, TVs, stereo radio, etc.).

The middle whip in your pic looks to have an appendage I don't recognize... Any brand name/model info on that?

One cheap way to trace is to first determine what works and what doesn't.

-Chris

Click to expand...

An appendage - you mean this? No idea what it is - maybe SSB?

Have you tried talking with the prior owner? Or perhaps your surveyor?

mvweebles said:

An appendage - you mean this? No idea what it is - maybe SSB?

View attachment 112205

Click to expand...

That appendage looks like a radar reflector to me. A lot of sailboats have that type attached to the standing rigging up high. (Makes you show up on other boat's radars better.) Never seen one on antenna like that, I think it would block the radio signals.

The 2 cables in the picture are both RG-6 used for off air television and the satellite TV antenna that is in the dome if that is what it is. The connectors on it are type F. On VHF antennas you typically see larger PL-259 or N type connectors.

I agree that the attachment on the antenna looks like a radar reflector. It could be an antenna tuner for a SSB, but they are normally in a series type connection with the antenna. If it is a radar reflector I would move it as it is not helping the VHF antenna any. The transmitting wire inside the fiberglass rod generally starts within 6 inches of the base.

Tom

https://www.defender.com/product.jsp?id=6857574

Look like a radar reflector.

No idea why a 3rd VHF antenna. Question to the forum. Can a regular VHF antenna also bennused for AIS transmit?

Weebles,

Yes it can, it’s just matched ideally to the AIS frequency. I use a Morad VHF antenna for my Class B and see no problems. I probably lose a little range, but less than if you used a splitter on the same antenna for a receive only AIS.

Tom

Thanks everybody for feedback. Yes the appendage is a radar reflector - maybe there's a better location for it, as suggested. Yes the dome on the radar arch is a TV receiver - we removed the TV and home theatre/sound system when we bought the boat, so it's redundant. (replaced with Fusion RA770 marine stereo system). The 2 coax cables were connected to the TV/sound system so at least one of those go to the dome. Not sure if the second one also goes to the dome or one of the aerials. It might be worth buying an adapter and seeing what happens if I plug those into the Fusion stereo for FM reception. Not sure if the TV dome would provide FM reception, or perhaps the 2nd one is connected to an aerial which would provide reception. Many other good ideas in this thread for me to consider as well - thanks again.

Turn everything on and disconnect cables on at a time and see which one stops working.

Yes, but the 2 cables which are already disconnected are the ones I'm most interested in.

TV cables. Perhaps from a cable box the PO took with him.

Lose the radar reflector. They don't work well under the best of circumstances.

For the coax, I can think of only a TV antenna. It's been years since I've had an external TV antenna on a boat (pre digital) but it didn't work well. You may want to try a cheap plastic antenna up high, assuming you can find the other end in your cabin.

Aim your antennas straight up and down, not at the angle of the arch. Better reception that way...

Pau Hana said:

Aim your antennas straight up and down, not at the angle of the arch. Better reception that way...

Click to expand...

+1

Vertical Aerials

LOL, agreed on the aerials. Old photo on the original post - I caught and corrected that pretty soon after the purchase!

Another consideration not mentioned is vhf is usually 50 ohm coax. Tv is usually 75 ohm. Vaguely interchangeable, but not recommended.

The dome is tv.

The 2 little mushrooms look like gps antennas but one MIGHT be satellite radio. Do you have a sirius subscription with your new fusion stereo?

Usually the little mushrooms will have some fine print on them somewhere identifying a brand. That would go a long way to iding them.

I do not think it is correct that radar reflectors do not work. I do think that there is a snake oil issue. Some reflectors do not work well, certain others do offer a level of protection. There are many publications citing test results of different configurations. Perhaps the OP's unit is junk - who knows? But SOLAS makes a strong statement regarding the use of reflectors.

"SOLAS V 19.2.1.7 requires vessels if less than 150 gross tonnage and if practicable, [shall have] a radar reflector or other means, to enable detection by ships navigating by radar at both 9 and 3 GHz."

Your ID shows that you are in Vancouver. Doesn't say where, but speaking generally, any boat operating in Vancouver requires a permanently mounted radar reflector.
Years ago Practical Sailor did a reflector comparison. The type that you presently heve came then in the tall skinny one that you have and in a shorter, fatter one. In the PS tests one of those tested out as one of the better reflectors, the other not well at all. Sorry but I don't recall exactly which won. When you get the chance, have a boater with radar report on the strength of his return from your boat. A permanent mount of the tall, skinny reflector requires something to support both ends. That may now be the sole remaining purpose of that third "VHF" antenna.
As for your coax, many boats have tried to keep up with rapidly advancing technology, resulting in runs of cable that become redundant. I would guess that is what you have.
Good call on making the antennas point vertically.
"There are 2 very small receivers on my radar arch " - Those are both GPS. Each should have a brand name "Garmin", "Lowrance", "Furuno" or other lesser known brands. You should be able to find a matching unit inside for each. If not, then an equipment upgrade failed to include removal of the redundant unit.
Good luck with your new baby.

koliver said:

Your ID shows that you are in Vancouver. Doesn't say where, but speaking generally, any boat operating in Vancouver requires a permanently mounted radar reflector.
Years ago Practical Sailor did a reflector comparison. The type that you presently heve came then in the tall skinny one that you have and in a shorter, fatter one. In the PS tests one of those tested out as one of the better reflectors, the other not well at all. Sorry but I don't recall exactly which won. When you get the chance, have a boater with radar report on the strength of his return from your boat. A permanent mount of the tall, skinny reflector requires something to support both ends. That may now be the sole remaining purpose of that third "VHF" antenna.

Click to expand...

I read the same test (or another like it, they've probably done more than one) and the funny thing is the cheapo $25 foil over foam Davis unit handily outperformed all the others. Only problem was it was so light weight it would probably blow away in 25 knots.

I fitted a Trilens passive reflector after a near miss from a fishing boat in thick fog 10 years ago. Back then the Echomax and Trilens were reported as being the best passive reflectors, and definitely better than the Davis type. If I were to do it today, I would definitely spring for an active type reflector which is what I think the OP has. IMO, apart from the SOLAS requirement, if you boat anywhere after dark or, especially, in fog, a reflector is an essential safety item. It complements your AIS and radar in helping you avoid others and helping others avoid you.

+1 on the trilens. Ran that and an active. The commonly used SSB antennas are very long. Sailboats commonly use glass terminals on their backstays in order to achieve sufficient length.

The “Mushrooms” are usually gps antennas (mine had 3) or perhaps Sirius (mine had 2). If you have a class B AIS, Then it must have its own GPS & may have it’s own antenna (which can look identical to the VHF antennas). The coax, as others have said, are almost certainly legacy tv antenna cables. Most technicians simply install completely new systems since they don’t want an unhappy customer if they reuse legacy equipment/cables/antennas which might fail. Similarly, in my experience, they never remove old cables or anything else that doesn’t hamper their installation- again because it’s time consuming and customers complain about the (unnecessary) cost.
You, however, will learn a tremendous amount about your new boat by following the wire runs and judiciously removing legacy stuff. I know I have. Be sure to pull a “messenger” line to leave in place for any hidden cable runs for future changes.

Good luck

Antennas

Thanks for the info. Here's a follow up question; Let's assume all 3 aerials are currently used: 2 for VHF radios and 1 for AIS. Any recommendations on hooking up an antenna for my FM stereo? I was hoping one of the three aerials was for a prior FM hook-up, but if that's not the case can I use a splitter and share an aerial with one of the VHF radios or is that not recommended.

Thanks!

I used a splitter for many years. Seemed to work fine. I've dispensed with FM radio altogether in favor of streaming from phone to a Bluetooth speaker.

https://www.hodgesmarine.com/sha435...MI1vj_-9iO7gIVCaGzCh0gLAhgEAQYASABEgJcbPD_BwE